Modern circuit technology involves the primary usage of printed circuit boards upon which multiple components are mounted. One of the major uses of printed circuit boards is for the mounting of pin grid array units which provide an integrated circuit having multitudinous connections which are output through connector pins on the underside. These pin grids arrays are mounted via the underside pins onto a printed circuit board and soldered (or inserted in sockets placed in the circuit board) into place in such a close knit fashion that it is practically impossible to make access contact with the underside pins once they are mounted on the printed circuit board.
It is very desirable and sometimes essential that there be methods of probing the pins of a pin grid array that is soldered or attached to a circuit board. One method for accessing the pins of the pin grid array is to access them from the solder side of the board. However, as obvious as this may seem, this method of access is not feasible due to the situation where the solder side is not accessible for probing due to proximity of other printed circuit boards and also the difficulty in locating and spotting specific pin locations in a relatively inaccessible area.
Another method of probing the pins of a pin grid array is to use what are known as "scratch pads" on the top surface of the pin grid array. However, again there are disadvantages and problems involved in this method, since "scratch pads" for probing may have to be built into the pin grid array by the manufacture at additional expense. In this situation, each scratch pad is etched on the top of the pin grid array and is connected to a corresponding pin via internal interconnections. This adds considerable expense to the pin grid array unit. And again unfortunately, in actual usage, the top surface of a pin grid array must very often be used to mount a heat sink which then makes access to the added scratch pads an impossibility.
In order to solve these various problems of pin probe accessibility in an economic and efficient manner, the present disclosure presents an access device unit printed on a flexible film circuit. This device is inserted between the printed circuit board and the pin grid array. Thereafter any inaccessible pin can be accessed by attaching a probe to the appropriate perimeter (external) contact pad on the flexible circuit which provides electrical connection to the underside pins of the pin grid array.